A 32-year-old man with a 6-year history of ulcerative colitis presents with bloody diarrhea and abdominal cramping. Colonoscopy reveals continuous mucosal inflammation with crypt abscesses and ulceration. Which is the most common site of involvement in ulcerative colitis?
A. Rectum and sigmoid colon
B. Jejunum and ileum
C. Cecum and ascending colon
D. Terminal ileum
Explanation
Most Common Site of Ulcerative Colitis
Key Point
Ulcerative colitis characteristically involves the rectum and sigmoid colon in the majority of cases, with proximal extension occurring in only a minority of patients.
Pattern of Involvement
Ulcerative colitis follows a continuous, retrograde pattern of inflammation:
Always begins in the rectum
Extends proximally in a continuous manner (no skip lesions)
Rectosigmoid involvement occurs in ~90% of cases
Pancolitis (entire colon) occurs in only ~20% of cases
Distinguishing Features from Crohn's Disease
Table
Feature
Ulcerative Colitis
Crohn's Disease
Most common site
Rectosigmoid
Terminal ileum
Pattern
Continuous
Skip lesions
Depth
Mucosa + submucosa
Transmural
Small bowel involvement
Never
Common (40%)
Ileal involvement
Only if pancolitis
Very common
High-YieldNEET PG
The rectum is ALWAYS involved in ulcerative colitis. If the rectum is spared, the diagnosis is not ulcerative colitis—consider Crohn's disease or other colitis.
Clinical Pearl
Patients often present with rectal bleeding and urgency because the rectosigmoid is the most inflamed region. Proctosigmoidoscopy alone may be sufficient for initial diagnosis in many cases.
Why Other Sites Are Less Common
Terminal ileum: This is the hallmark of Crohn's disease, not ulcerative colitis. UC does not involve the small bowel unless pancolitis extends to the ileocecal valve.
Jejunum: Never involved in either UC or typical Crohn's disease.
Cecum and ascending colon: These are involved only when disease extends proximally from the rectosigmoid (pancolitis), which is less common than isolated rectosigmoid disease.
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